A number of processes for the impregnation of foams and foam particles have already been described. In such processes, the foams are impregnated with a reactive component (for example with polyisocyanates) and are subsequently reacted with other reactants, (for example polyols, polyamines or vapors of diamines). Typical of such processes are those described in German Offenlegungsschriften Nos. 3,039,146 and 2,131,206, Japanese Pat. No. 50-103 571, French Pat. Nos. 1,587,855 and 1,574,798, and U.S. Pat. No. 2,955,056.
Foams can also be exposed to a liquid having a swelling action. Polyurethane reaction components can then be reacted in the swollen mixture, permitting solidification and rigidification of the foam and optionally allowing inlays to be placed in the swollen foam matrix. Typical of such processes are those described in French Pat. Nos. 1,341,717, 1,587,855, 1,574,798 and German Auslegeschrift No. 1,911,645. Such matrix foams exhibit typical foam properties, although they are somewhat different in hardness, elasticity or chemical and mechanical properties.
A number of other patents describes the adhesion or the pressing of foam particles (preferably polyurethane flexible foam waste) using polyisocyanates, isocyanate-terminated prepolymers and, polyols, polyamines, water or other reactants, optionally with the addition of cork, fibers, cellulose dust, flame-proofing agents, pigments, powdered metals or carbon black, to form novel composite materials. These composite materials are used, for example, as insulating and damping plates, linings, mattresses or molded articles. Suitable processes are described, for example, in British Pat. Nos. 1,337,413 and 1,540,076; U.S. Pat. No. 4,254,177; Japanese Pat. No. 57/028 180 and German Offenlegungsschriften Nos. 2,940,260, 3,213,610, 2,908,161 and 3,120,121.
To date, only the production of block foam from polyurethane foam particles, 10 to 20% by weight of isocyanate compounds, up to approximately 10% by weight of other fillers and small quantities of water have achieved any commercial significance. In this case, the filler consists mainly of color pigments in order to impart a uniform coloring to the composite foam which can consist of foam pieces of differing colors. The water used during the production of the composite foam reacts with the polyisocyanate to form polyurea groups with evolution of carbon dioxide. The quantity of water is selected in such a way that it corresponds approximately to the stoichiometric requirement of the isocyanates, but at most is present in only a relatively small excess since the removal of moisture from the 40 to 60 cm thick composite blocks would cause problems.
The cuttings or scrap produced in industrial quantities when cutting flexible block foam to shape, are preferably used as raw material for the composite foams. The composites, which have a relatively high bulk density, are used as mattresses or elastic carpet underlays. Cuttings (or scrap) are available as scrap polyurethane foam at low cost and in such large quantities that only a proportion thereof can be used for this purpose. The problem of finding an ecologically reasonable and economically advantageous use for the excessive industrial quantities of polyurethane foam scrap has existed for a long time. Elimination of the scrap by burning or dumping is extremely difficult industrially due to the extremely great volume of the scrap.
Water-swollen polyurethane(urea) gels which are either homogeneous or expanded by CO.sub.2 generation are also known and described in German Offenlegungsschriften Nos. 2,347,299 and 2,521,265. Such gels are described as containing up to 50% by volume of fillers such as silicates, silica, aluminum oxides, tin oxide, antimony trioxide, titanium dioxide, graphite and graphited coal, retort coal, carbon black, powdered cement, color pigments, fibers and cellulose powder in addition to surfactants or nutrients. The use of foam particles is not described. In this case, the water absorbability of the gels is due to the use of hydrophilic polyurethanes containing 40% or more by weight of oxyethylene sequences.
Water-swollen polyurethane gels, which can contain from 20 to 80% by weight of abrasives such as aluminum oxide, cerium oxide, tungsten dioxide, boron carbide, silicon carbide, carborundum, asbestos dust or diamond dust; graphite; microglass beads; short fibers with an inorganic or organic base, fungicides, dyes or color pigments are also known and have already been described in German Offenlegungsschrift No. 3,151,925. Solid fillers of this type, however, are not water absorbing and cannot display high-water absorbability.
German Offenlegungsschrift No. 3,103,499 describes substantially water-free, polyurethane gel masses using polyols as dispersants. The gels can contain active ingredients, dyes, pigments, fibers, inorganic fillers, powdered metal, activated carbon, cellulose powder and silicas. These polyol-containing gels are not desirable since they tend to give up a large proportion of the dispersed polyol.
The embedding of cells capable of growth in polyurethane hydrogels is also known; see, for example, Tanaka et al., European Journal of Applied Microbiology and Biotechnology, 7, (1979) from page 351. A process for the production of hydrophilic gel-like or foamed biocatalysts with a high charge of enzyme-active substance by polymeric inclusion of complete cells, of cell fragments or enzymes, by mixing an aqeuous suspension of the enzyme-active substance with hydrophilic polyisocyanates to form a highly enzyme-active hydrophilic polyurethane network in block or bead form is described in German Offenlegungsschrift 2,929,872. Further publications pertaining to the prior art are noted on page 7 of the Offenlegungsschrift.
In the polyurethane gels according to the prior art, it is necessary to build up hydrophilic polyurethanes using polyethers with high ethylene oxide contents in order to achieve an adequate water absorbability. Problems of reactivity of the hydrophilic polyether polyols (which usually exhibit high activity) and problems in the mechanical gel strength when using highly hydrophilic polyether polyols often arise. In addition to the high price of polyurethane gel compositions which are made up in this way, such gels possess only a limited water storage capacity.